Could I ask why you'd have hoped for open source? If it's any consolation, I'm making the API completely open, and I'd have no problem with custom clients. In fact, I may even consider open-sourcing the default web-app client. But as for running it as a SaaS rather than distributing the whole thing as open source, I feel like the whole project will have a brighter future if it's set up in a sustainable way like this, and subscription fees can be invested back into the product, towards marketing, development, scaling etc.